The present disclosure relates to a needle assembly that is fitted to a drug ejection portion of a drug container such as an injection syringe to use, and a drug injection device that includes such a needle assembly.
In some drug injection devices, a syringe that contains an injection drug, and a needle assembly that includes a needle are separately formed, and the needle assembly is attached to a drug ejection portion at a cylindrical tip of the syringe and is used for injection. See, e.g., JP 2011-212185 A.
A needle assembly is generally attached to a drug ejection portion by taper fitting. More specifically, the drug ejection portion is formed in a male tapered shape (truncated conical shape) whose outer diameter continuously becomes smaller toward a distal end. The needle assembly is provided with a fitting portion including a cylindrical hole, and this fitting portion is formed in a female tapered shape (truncated conical shape) that has a size matching the drug ejection portion and whose inner diameter continuously becomes smaller from an opening including the cylindrical hole. The male tapered shape and the female tapered shape are formed at the same taper rate. By pressuring a drug ejection tube and pushing the fitting portion, surfaces of the tapered shapes press against each other and are fixed in liquid-tight manner.